Hormonal control of the reproductive cycle of the Cynomolgus macaque is of particular interest in the development of timed-mating for embryo collection studies. In this investigation, which employs laparoscopic visualization of ovarian activity and radioimmunoassay of serum to confirm endocrine function, attempts are being made to synchronize female macaques to ovulate and breed at similar times. Progesterone is administered to mature animals disregarding the stage of its natural menstrual cycle. Following progesterone withdrawal, ovarian function is monitored serially in each animal by laparoscopy and assay of frequently obtained blood samples. At the appropriate time, females are paired with breeding males until ovulation and copulation are confirmed.